1. Field of the Invention
The invention relates to an apparatus and method for estimating a turning characteristic of a vehicle.
2. Description of the Related Art
An apparatus for estimating a turning characteristic of a vehicle such as an automobile or the like, is known which detects a vehicle speed, a steering angle, and a yaw rate using sensors when the vehicle is running, and estimates a stability factor as the turning characteristic of a vehicle based on those detected values. An example of such art is disclosed in Japanese Patent Laid-Open Publication No. 10-258720.
According to that apparatus, because the stability factor is estimated based on the actual turning state of the vehicle, the standard yaw rate can be calculated more accurately than when it is calculated using a stability factor that is set at a fixed value. As a result, it is possible to accurately execute vehicle control based on the standard yaw rate and the actual yaw rate of the vehicle.
The apparatus of the aforementioned publication calculates the stability factor only when the lateral acceleration of the vehicle is equal to, or less than, a predetermined value. However, there is no reference of that apparatus estimating a transfer function between the standard yaw rate of the vehicle and the actual yaw rate of the vehicle, and then estimating a turning characteristic of the vehicle, such as the stability factor, based on that transfer function. Accordingly, in this respect there remains room for improvement in the foregoing apparatus.
For example, when estimating the transfer function between the standard yaw rate of the vehicle and the actual yaw rate of the vehicle as a first order delay transfer function and then estimating the turning characteristic of the vehicle, such as the stability factor, based on that transfer function, it is necessary to estimate the transfer function appropriately. In order to estimate the transfer function appropriately, however, the transfer function must be estimated based on vehicle running data that is suitable for making the estimation.
Therefore, in the actual turning state of the vehicle there are times when the turning characteristic of the vehicle is unable to be estimated appropriately due to the fact that the vehicle running data is not always necessarily suitable for appropriately estimating the transfer function so the transfer function is not always estimated appropriately. Also, when the transfer function is estimated as a first order delay transfer function, it is necessary to select the running data suitable for estimating the transfer function while ensuring continuity of the running data.